BACKGROUND: Continuous quality improvement (CQI) collaboration has not eliminated the morbidity variability seen among neonatal intensive care units (NICUs). Factors other than inconstant application of potentially better practices (PBPs) might explain divergent proficiency. OBJECTIVE: Measure a composite morbidity score and determine whether cultural, environmental and cognitive factors distinguish high proficiency from lower proficiency NICUs. DESIGN/METHODS: Retrospective analysis using a risk-adjusted composite morbidity score (Benefit Metric) and cultural survey focusing on very low birth weight (VLBW) infants from 39 NICUs, years 2000-2014. The Benefit Metric and yearly variance from the group mean was rank-ordered by NICU. A comprehensive survey was completed by each NICU exploring whether morbidity variance correlated with CQI methodology, cultural, environmental and/or cognitive characteristics. RESULTS: 58 272 VLBW infants were included, mean (SD) age 28.2 (3.0) weeks, birth weight 1031 (301) g. The 39 NICU groups' Benefit Metric improved 40%, from 80 in 2000 to 112 in 2014 (P CONCLUSION: Cultural, environmental and cognitive characteristics vary among NICUs perhaps more than traditional CQI methodology and PBPs, possibly explaining the inconstancy of VLBW infant morbidity reduction efforts. High proficiency NICUs foster spirited team work and camaraderie, sustained learning opportunities and support of favourable staffing that allows problem solving and widespread involvement in CQI activities.